Carbohydrates are often polymeric and are named, grouped and classed according to the identity of the composed monosaccharide, the number of monomeric units, and the carbon position of the covalent bonds linking each monosaccharide.
Currently a wide range of methods for detection, identification and quantification of carbohydrates are known and applied across all industries. However, few of these methods have sufficient resolution to identify the precise molecule. This is due to the inherent nature of the chemical structure of polysaccharides, which are large macromolecules composed of a small group of identical subunits. As a result of this repetitive nature, carbohydrates do not commonly present unique epitopes or binding surfaces for easy detection with probes. The lack of unique epitopes and difficulty of detection is in contrast to proteins, which have several levels of structural conformations and unique qualities in addition to the primary amino acid sequence. In contrast to proteins, antibody based detection systems are rarely effective when used for carbohydrates.
Identification of carbohydrates is commonly performed by indirect means and is biased towards soluble carbohydrates. For example, the carbohydrate identity may be uncovered by an initial monomerization step, followed by an identification step in which each monomer and the percentage of each monomer present is identified. The gained monomer information is then fed back into a determination step in which the identity of the original carbohydrate is determined.
Other common techniques for carbohydrate analysis use a combination of chromatography (e.g. thin layer chromatography, gas chromatography, high performance liquid chromatography) and detailed chemical analysis by electrophoresis or mass spectrometry of polymers or monomers. Often, mass spectrometry is used in combination with a prior step of separation to purify a mixture before analysis. In addition, monomerization of the polysaccharide chain is often a requirement for analysis of larger carbohydrates. While highly accurate, the singular and/or sequential use of the above methods can be slow and cumbersome, and requires a significant amount of expertise (Zidková J and Chmelík J, J. Mass Spectrom. (2001), 36(4):417-21).
In nature, carbohydrates are as ubiquitous as proteins. They function both as substrates in metabolism, as structural macromolecules, and as ligands/targets for adhesion, signaling and in many biological interactions. In pharmaceutical industries as well as other industrial settings, carbohydrates represent several high grossing products in the market. These products range from drugs to foods and supplements to new polymers for ‘green’ materials. A simple sensitive method for carbohydrate identification and quantification is anticipated to be of great usefulness in these settings.
WO2010/044744 A1 discloses novel thiophene compounds for use in in vivo imaging of amyloid or aggregated forms of proteins. The document discloses randomly polymerized polythiophenes, as well as oligomeric thiophenes of defined length, that bind to and enable detection of such proteins. The disclosed oligothiophene compounds are for example useful for diagnosis of Alzheimer's disease and other diseases involving aggregated or misfolded proteins.
Åslund, A et al (ACS Chem. Biol. (2009), 4(8):673-684) discloses pentameric luminescent conjugated oligothiophenes for selective identification of protein aggregates. The disclosed LCOs can be utilized as research tools for studying protein aggregation diseases such as prionic diseases and Alzheimer's disease.
Klingstedt, T et al (Org. Biomol. Chem. (2011), 9:8356-8370) discloses a library of luminescent conjugated oligothiophenes of different lengths as well as their method of synthesis. The disclosed luminescent conjugated oligothiophenes are useful for selective identification of protein aggregates, They facilitate the study of protein aggregation diseases and could also be utilized for the development of novel diagnostic tools for such diseases.